Tank cars have been used for many years to transport a wide variety of commodities including liquids, gasses and other fluids. The contents of a tank car may sometimes be potentially hazardous if appropriate safety precautions are not taken. Also, the contents of a tank car may be valuable and subject to theft or misappropriation.
Most tank cars are designed with an access opening or manway nozzle located in the upper portion of the associated tank, proximate a midpoint between opposite ends of the tank car. A manway cover plate is typically bolted or otherwise secured to the opening at the top of the nozzle to function as a liquid-tight closure and to allow only limited access by personnel to the interior of the tank. Various pipes, valves, fittings and other components are also often located in the vicinity of the manway to control adding and discharging lading from the tank car. The valves, fittings and other components are typically selected based on characteristics and properties of the commodity or lading being transported.
Valves, fittings and other components are often mounted on the manway cover plate of modern pressurized tank cars. Pressure car fittings typically include two “liquid or fluid” valves for loading and unloading of an associated commodity. Respective check valves and induction piping are also provided with respective loading and unloading valves. One or more vapor valves, gauging devices and safety relief valves may also be mounted on the manway cover. Some tank cars may have smaller valves for drawing samples of lading and thermal wells for measuring the temperature of the lading. Non-pressurized tank cars may also have similar valves and fittings mounted on a manway cover similar to a pressurized tank car.
Various types of protective housing assemblies or dome structures are often disposed on the upper portion of a tank car adjacent to the manway to protect associated piping, valves, fittings and other components. All pressurized tank cars are required to have such protective housing assemblies or dome structures covering any pipes, valves, fittings and other components located on an upper portion of the pressurized tank car. A relatively thick, steel ring or cylindrical portion is often attached by bolting to the cover plate to protect the valves, fittings, and other components in the event the tank car is derailed and overturns.
In the event of a high speed derailment, the forces acting on the overturned tank car may be sufficient to remove the protective housing assembly from the tank car and expose the enclosed valves, fittings, and other components to damaging impact forces. These impact forces may result in the shearing off or damage of exposed components. If a component is damaged or removed, the contents of the tank car may be released to the ambient environment causing a hazardous condition and/or loss of the contents of the tank car.